1. Field of the Invention
The invention relates generally to the field of materials. More particularly, the invention relates to synthesis of layers, coatings or films. Specifically, a preferred implementation of the invention relates to the synthesis of layers, coatings or films using a template. The invention thus relates to a layer, coating or film synthesis technology of the type that can be termed template enhanced.
2. Discussion of the Related Art
A plethora of methods have been used for the synthesis of films (coatings) composed of materials from the CIS (copper indium selenide) material system and related alloys, but each of the previous methods has characteristics that limit their applicability to the economical manufacture of films with properties suitable for application to optoelectronic devices, such as photovoltaic (PV) devices. PV devices require an optical absorber that also provides sufficiently long minority carrier lifetimes to enable the collection of the minority carriers by the electrodes in the device's structure without excessive recombination. In all semiconductor materials minority carrier lifetimes are dependent on the defect structure of those materials. The control of defect structure is critical to the successful manufacture of PV devices. Similarly the defect structure of high-temperature superconductors, electroluminescent phosphors, and other (opto-)electronic materials control the physical properties that determine their efficacy for their respective intended uses.
Thin film optical absorbers are more economical than thick film absorbers or coatings because they require a smaller amount of the precursor materials than thick films or coatings. The formation of thin films with desirable defect properties is predominately determined by the method by which they are synthesized. Early efforts to fabricate thin film CIS PV devices that relied on the steady-state co-deposition of the constituent elements copper, indium, and selenide were not very successful. The first efficient thin film CIS PV devices were achieved by a two-step process that relied on the sequential deposition of two layers onto a substrate at high temperature, each with different composition. These layers reacted and intermixed to yield a nominally uniform composition throughout their combined thickness, and resulted in films with desirable defect structures. Variations of this method have been demonstrated, based on different temperatures, numbers of layers, and compositions thereof. Other fundamentally different approaches have been described that rely on, for example: (1) heating stacked layers of the metals (e.g., copper, indium and gallium) and selenide that have been sequentially deposited at low temperatures, (2) thermal reaction of metallic layer precursors in hydrogen selenide or selenide vapor, (3) thermal reaction of oxide particulate precursor mixture layers at high temperatures, and (4) thermal reaction of binary (Cu,Se) and (In,Se) precursor layers.
An economical process for the manufacture of thin films of these sorts of non-stoichiometric multinary compounds needs to both efficiently use raw materials and be rapid (for low cost), but must be flexible to enable control of the defect structures required for high performance. None of the methods in the prior art provide an optimal combination of these features.
Heretofore, the requirements of efficient raw material utilization, rapid fabrication, and flexibility for optimization of defect properties referred to above have not been fully met. What is needed is a solution that simultaneously addresses all of these requirements.